Extreme, Dangerous Heat Wave to Expand Coast-to-Coast

Millions of Americans have already recorded temperatures in the 90s and even the 100s in some locales, and the heat will persist into the new week across the Northeast and central US as a new “heat dome” builds over the region. Eventually, a coast-to-coast heat event will develop for a brief time by the end of the week.

Through the first half of the week, a new ridge of high pressure will develop over the Northeast. This ridge will likely exceed geopotential heights of 594 decameters, which is record-breaking strength for parts of the region. Then by mid-week, this ridge will expand and intensify, building back into the central US. By this point in time, heights will approach 600 decameters. It’s not until the end of the week when the center of this “heat dome” traverses across the country and ends up over the West while the East Coast cools back down to average — for a brief time — thanks to a cold front.

So you may be asking: what are geopotential heights? According to our Chief Meteorologist Joshua Feldman, “The thicker the layer between the surface and any layer of the atmosphere, the warmer the average temperature must be. The 500 millibar surface is significant because roughly half of the atmosphere’s mass is contained beneath this layer.” Heights are a good indicator at predicting these extreme heat events and frankly any type of air mass.

As a new upper-level ridge begins to reinvigorate over the Northeast and Midwest beginning Monday, the effects of Saturday night’s cold front will start to become unnoticeable as hot air streams back in from the south. High humidity will remain a constant battle across this part of the country with the exemption for the Upper Midwest. Dew points in this area will be in the 50s and 60s while 70s dominate the remaining areas. If you’re not familiar with dew points, the main thing to know is that temperatures less than 55 degrees indicates pleasant humidity levels, around 65 degrees means sticky, and around 75 degrees is oppressive.

Another dangerous component to this prolonged heat wave in parts of the Midwest and Northeast is the little relief overnight. Widespread low temperatures into the 70s will keep the air conditioners in overdrive, and for those that rely on the cool nights who don’t have an AC unit may feel overwhelmed by the heat.

High temperatures across the central and southern Plains as well as up and down most of the East Coast will be in the 90s on Monday. Texas will absolutely be baking with highs in the 100s, but that’s actually common for this time of the year. On the other hand in the Mid-Atlantic and New England, some locations will likely get into the low 100s, especially in the metropolitan areas, which is up to 25 degrees above average. The sea breeze will keep the southern and eastern coasts of New England cooler into the 80s, however. In between across the Midwest and Gulf Coast states, temperatures will generally be in the mid to upper 80s with a few 90s sprinkled in there.

The “heat dome” will continue to expand on Tuesday with the possible appearance of a 597-plus decameter ridge over the Northeast. By this point in time, many cities will have verified a heat wave. An official heat wave is when temperatures are 90 degrees or greater for at least 3 consecutive days. Not only will it be a heat wave, it will be a prolonged one. Once it comes to an end, some cities may come in with an 8-day-long, 90-plus degree stretch, but it will likely not be record-breaking. The record in New York City will remain at 12 days from 1953 while in Hartford it will come close. Their record is 10 days from 2016 and 1995.

In terms of high temperatures on Tuesday, it will not be as hot as the previous days for most locations. Temperatures will follow a similar setup as on Monday, although it will be a few degrees warmer in the central US. Highs will be right around 90 across the Midwest down through the Gulf Coast. It will be several degrees warmer to the east and west. The central and southern Plains will feature highs generally into the 100s. The Mid-Atlantic will deal with highs mainly in the low to mid 90s. Even the coast should be hot with 90-plus degree temperature thanks to an offshore flow. Highs in the 100s will also be possible in central portions of New England, including Hartford.

Dew points on Tuesday will be very gross, reaching widespread levels into the 70s. Let’s say the high temperature is 90 degrees and the dew point is 75 degrees. That will translate to a heat index of 101 degrees, which is dangerous for some people. In many areas, these temperatures aren’t too hot, but it’s the persistence of this heat event as well as the oppressive humidity that’s the “deal-breaker.” Across the corn belt region, the process of transpiration will be very common, which is when water evaporates from the plants. That added water will make dew points even higher.

By Wednesday, it will be quite difficult to find temperatures cooler than 90 degrees east of the Continental Divide. The only lucky locations will be in parts of northern Plains, Great Lakes, and Appalachian Mountains. Otherwise, widespread highs into the 90s can be expected across the eastern and central US. 100s will even be possible in parts of the Plains and Ohio River Valley.

This will then turn into a nationwide heat event on Thursday as the “heat dome” takes over the entire continuous US. Temperatures will be above average, especially in the Northeast. Due to multiple disturbances riding along its southern extent, which will keep temperatures close to seasonable near the Gulf Coast. Also an onshore flow off from the Pacific Ocean will keep the immediate West Coast cool.

High temperatures on Thursday will be in the 80s and 90s coast-to-coast. Highs near 90 degrees will dominate across most of the eastern and central US. In the lower elevations of the West, high temperatures will range from the 70s in the Northwest to the 110s in the desert Southwest. If you want to stay cool, head to the Colorado Rockies where it will be in the refreshing 60s.

Beginning Friday, a cold front, containing showers and thunderstorms, will move through parts of the Great Lakes and Northeast, lowering temperatures down into 70s and 80s. To the south, high temperatures in the upper 80s to 90s will remain dominant across the remainder of the central and eastern US. Temperatures will be very similar as Thursday across the West as they will be on Friday.

Looking ahead to next weekend, it’s too early to discuss the forecast in detail at this point in time, but much of the eastern US will cool off for a few days with temperatures very seasonable. Meanwhile across the western US, it will be hot with temperatures above average across most locations thanks to the massive upper-level ridge of high pressure directly overhead.

Jackson is Head of Content at WeatherOptics and produces several forecasts and manages all social media platforms. Previously, Jackson forecasted local weather for southwestern Connecticut, founding his website, Jackson's Weather, in the March of 2015. He is currently studying Meteorology and Broadcast Journalism at the University of Miami.